The present invention relates to precipitation polymerization processes for making essentially non-crosslinked polymers which are prepared from N-vinyl acetamide monomer and which have reduced levels of non-polymerizable contaminants, particularly acetamide.
In processes for making polymers, processes had been utilized to substantially reduce residual monomer levels. For instance, it is known to polymerize a polymer solution/emulsion on a powder bed at high temperature, thereby removing the solvent from the precipitating polymer. The monomer level is reduced by post-polymerizing unreacted monomer. There is no mention of methods for removing non-polymerizable contaminants which may be present in the resultant polymer as an artifact of the monomers and/or processes used to prepare the monomers and polymers. Such contaminants may include, for example, raw materials used to prepare the monomers, intermediates which are formed during manufacture of the monomers and degradation by-products of the manufacture of the monomer. Additionally, non-polymerizable contaminants may be introduced via raw materials used to prepare the polymers, such as the monomers themselves, chain transfer agents, initiators and the like. So while methods for reducing residual monomer levels in polymers generally are known, methods for removing non-polymerizable contaminants from polymers have not been reported.
Polymers having reduced levels of contaminants particularly are desired and/or required for end-use applications such as cosmetics for application to skin, hair care products and pharmaceuticals. Therefore, it would be advantageous to develop a precipitation process which not only results in polymers having low residual monomer levels, but also having low non-polymerizable contaminant levels.
The precipitation processes of the present invention result in polymers which not only have reduced residual monomer levels, but just as important, exhibit significant reduction in the levels of non-polymerizable contaminants such as those discussed herein.
The present invention is directed to precipitation polymerization processes for the manufacture of essentially non-crosslinked polymers prepared from N-vinyl acetamide monomer, which polymers exhibit reduced levels of non-polymerizable contaminants, particularly acetamide. The process comprises the steps of contacting the N-vinyl acetamide monomer with a polymerization medium comprising a diluent selected from the group consisting of ethyl acetate and acetone and a free-radical initiator, under conditions effective to polymerize the N-vinyl acetamide monomer (NVAM), thereby forming a precipitate of poly(vinyl acetamide) polymer (PVAM) in the polymerization medium; and isolating the precipitated PVAM from the polymerization medium.